This invention relates to a method of etching a surface of an article using grit blasting.
Grit blasting is widely used for etching a surface of an article with a desired image. Steel grit, sand, aluminum oxide or other abrasive material can be propelled against the surface of the article. The article can be constructed of a variety of materials such as glass, stone, ceramics, wood, synthetic resin, metal or leather. To etch the image onto the article, a mask having a pattern corresponding to the desired image can be adhered to the article, followed by etching vacant portions or voids of the image by grit blasting. The present invention is directed to an improved method of etching a surface of an article.
Grit blasting has been effected in the past by employing a pattern mask prepared manually from rubber or paper and attaching the pattern mask to the article to be etched by employing an adhesive. This method is time consuming and cannot be used to etch fine image details on a repetitive basis.
In the past, surfaces of articles have also been etched by adhering an expensive metal template to the surface and grit blasting the template.
The surface of the article can also be etched by silk screen printing an image in relief onto a very fine sticky backing paper. This method requires a very strong ink image. The sticky backing paper is then dampened and then adhered to the surface. The image is then grit blasted. The grit material must, however, penetrate through the paper and its adhesive before affecting the surface. During this time, the ink image must withstand the grit blasting. This method is expensive for short runs and is best suited for long runs (etching the same image on hundreds of different articles).
Another prior art method of etching a surface of an article consists of silk screen printing a thick reverse image onto a carrier sheet and allowing the image to dry. An adhesive is then sprayed onto the image side and the image is then transferred onto the surface to be grit blasted. This method is also expensive for short runs.
U.S. Pat. No. 4,456,680 (Nakamura et al.) discloses a process for preparing a mask for grit blasting. The mask, carried on a destroyable film layer, is adhered to the article to be engraved and is then grit blasted. However, before the grit blast material reaches the article to be engraved, it must penetrate through the destroyable film layer, the mask being disposed between the destroyable film layer and the article to be engraved. The grit blast material must therefore penetrate through the destroyable film layer before the image is engraved onto the surface and accordingly the mask itself deteriorates as the grit blast material penetrates through the destroyable film layer.
U.S. Pat. No. 4,587,186 (Nakamura et al.) is a continuation-in-part of the Nakamura U.S. Pat. No. 4,456,680. The Nakamura U.S. Pat. No. 4,587,186 has the same difficulties as the Nakamura U.S. Pat. No. 4,456,680, although in the later patent the destroyable film layer is weaker so that it is easier to penetrate through. However, even in the Nakamura U.S. Pat. No. 4,587,186 the mask will deteriorate as the grit blast material penetrates through the destroyable film layer. In addition, the Nakamura U.S. Pat. No. 4,587,186 discloses a thicker photosensitive material and thus more light scattering will take place upon exposure through the image bearing transparency and his material must be thick enough to withstand a certain degree of grit blasting. The light scattering effect has a tendency to thicken or broaden the finer areas in an image, thus reducing resolution of fine detail.
U.S. Pat. No. 4,430,416 (Goto et al.) discloses a transfer element for sand blast carving. The Goto element includes an intermediate resin layer which must be penetrated by the sand blast material prior to etching the surface of the article. The mask element is of a substantial thickness which could result in an inability to produce a fine image.
U.S. Pat. No. 4,193,797 (Cohen et al.) discloses a method for making photo resists. The photo resist is mainly for acid etching and would not be suitable for grit blasting.